This research project is designed to identify and quantitate those factors which determine the oxygen uptake of normally circulated mammalian skeletal muscle. The experiments will be mainly performed on dog muscles. The main goals of the current project period are to identify the relationships of blood flow and of blood carried substances to oxygen uptake, and to establish the quantitative roles, if any, of the mechanical aspects of contractions, length, load, shortening and work, to oxygen uptake. In addition, there will be studies of the interaction between blood flow, and the substances in blood, to contraction mechanics and vice versa. Therefore, these studies will examine possible mechanisms of local control of blood flow.